In order to withdraw a small amount of blood from a body part (usually the finger or the earlobe) for analytic-diagnostic purposes, lancets are used which are punctured into the corresponding body part. If the lancets are punctured manually into the skin in order to generate a wound, specially trained staff is necessary. In any case, the puncturing procedure generates considerable pain.
For a long time already, blood withdrawal systems are used which consist of a puncturing device and associated lancets, adapted to the corresponding device. A housing of the puncturing device contains a lancet drive for mechanically driving the lancet into the skin. Normally a spring is used as drive element for the puncturing movement. In an early development phase very simple designs were used, wherein the lancet was fixed directly to the end of a pressure spring located in a housing of longitudinal shape (e.g. U.S. Pat. No. 4,469,110).
Such blood withdrawal systems, however, did not meet the high requirements to be fulfilled if a regular monitoring of certain analytical blood values is necessary. This is particularly true for diabetics who must control their blood glucose level frequently in order to maintain it continuously within certain target limits, by the adaptation of insulin injections with respect to the demand (which varies strongly depending on food intake and physical activities). Extensive scientific investigation proved that an intensive therapy with at least four blood analyses per day results in a dramatic decrease of the most severe late damages of Diabetes Mellitus (for example, a retinopathy with subsequent ablepsia of the patient).
However, such an intensive therapy requires a blood withdrawal with as little pain as possible. Several blood withdrawal systems were developed with the objective to achieve an improvement in this respect. Examples for this development are described in the subsequently discussed publications.
The design described in U.S. Pat. No. 4,924,879 features a spiral driving spring acting upon a rotor the rotation of which is converted, by means of a connecting rod, to a puncturing and retraction movement of the lancet. The pain is supposed to be decreased by the high speed of this movement. However, this design requires precisely machined metal parts and is expensive and relatively bulky. Another disadvantage of this design is the fact that during cocking of the lancet drive the lancet protrudes from the outlet opening, thus resulting in danger of injury.
U.S. Pat. No. 4,924,879 describes a design wherein the necessary connection between a drive element (realized as a leaf spring or a spiral spring) and the lancet is formed by two levers connected to each other by means of a swivel joint. One of the levers is connected, with its end facing the lancet, to the lancet by means of a second swivel joint, whereas the other lever is connected to the housing by means of a third swivel joint. The swivel axes of all three swivel joints are parallel to each other. In the cocked state, the toggle joint formed by the two levers is in a first bent position. After actuating a release button, it is moved by the force of the drive spring via a straight position to a second bent position, in which the first swivel joint is located, with respect to the initial position, on the other side of a plane defined by the puncture path of the lancet and the axis of the second swivel joint. In this design, too, the lancet protrudes from the outlet opening during the cocking process.
Blood withdrawal systems with the lancet drive described in U.S. Pat. No. 5,318,584 are used extensively. The users in particular appreciate the unsurpassed low level of pain. The core element of this drive is a rotor the rotor axis of which coincides with the longitudinal axis of the oblong (pencil-shaped) device. This rotor is driven by a coaxial spiral spring. Its rotational movement is converted to the required translational movement of the lancet by means of a cam control. The design of the cam control allows to cock the device without protrusion of the lancet tip from the housing. The rotation of the rotor around the longitudinal axis of the device minimies vibrations and stabilizes the puncturing process. However, the design consists of many parts with complicated shapes and therefore it is rather expensive. A newer version of a blood withdrawal system with a rotor rotating around the longitudinal axis is described in EP 1034740 A1.
In EP 1090584 A2 a further design of the rotor principle is described which reduces the constructive expense by using a drive rotor with a special shape, wherein the rotation of the rotor is caused by the force of the drive spring pressing against a correspondingly shaped pressure surface of the drive rotor. In this case too, the movement of the drive rotor is converted into a corresponding movement of the lancet by means of a cam control. This design requires a relatively wide housing form which is considered unfavorable by many users.